Conventionally, there are well-known methods for fabricating an optical fiber preform, including an MCVD method (Modified Chemical Vapor Deposition Method) and an OVD method (Outside Vapor Deposition Method). These methods involve synthesizing in succession a number of glass particle deposited layers radially on the inner or outer wall of a starting material of cylindrical or columnar shape to form a predetermined radial refractive index distribution (also referred to as a refractive index profile) and to fabricate a glass preform for drawing. Herein, the optical fiber preform means a vitreous body having substantially the same refractive index distribution as the optical fiber, in which an outside cladding layer may be further provided by such as a VAD method, an OVD method or a rod-in collapse method.
However, to fabricate a preform for optical fiber having a complex refractive index profile structure in which there are a plurality of maximal points and minimal points in the refractive index profile, such as a dispersion compensating fiber, a dispersion shifted fiber, or a dispersion flatted dispersion shifted fiber, the above manufacturing method for optical fiber preform has a problem that the optical fiber preform may be difficult to produce at high yield because the refractive index profile has a little tolerance for excellent characteristics. Therefore, the preform for optical fiber with complex profile had a problem that the manufacturing cost may be high.
This invention has been achieved in the light of the above-mentioned problems, and it is an object of the invention to provide a manufacturing method for an optical fiber preform and a manufacturing method for an optical fiber in which the optical fiber with a complex refractive index profile is produced at high precision, and an optical fiber.